プログレッシブ和英中辞典(第4版)の解説
たしか【確か】
❶〔確実〕確かな certain; sure（▼certainとsureはほぼ同意だが，certainの方が客観的で確実性が高いことが多い）
確かな証拠
positive evidence
彼が早い汽車に乗ったのは確かだ
It is certain that he took the earlier train.
その病気の確かな治療法
a sure cure for the disease
この問題が試験に出るのは確かだ
This question is sure to be on the test.
確かにお便りを拝見しました
Your letter has been received and duly read.
彼は確かに頭はよいが，あまりに利己主義だ
He is bright, indeed [to be sure], but too selfish.
確かに彼はそれを知っている
「I'm certain (that) [I'm sure (that)/I have no doubt that] he knows all about it.
確かに一万円札はくれたが，にせ札だった
He 「gave me a ten-thousand-yen bill all right [did give me a ten-thousand-yen bill], but it turned out to be counterfeit.
❷〔信頼できる様子〕確かな reliable
この情報は確かな筋からのものだ
This information came [is] from a reliable source.
彼女の料理の腕は確かだ
Whatever she cooks [makes] is sure to be good.
あの医者の腕は確かだ
He is a reliable doctor.／That doctor can [is to] be trusted.
❸〔健全・正常な様子〕確かな sound
頭はまだ確かだが目と耳が衰えてきた
His mind is still sound, but his eyesight and hearing are failing.
君，気は確かかね
Are you sure you're in your right mind?
❹〔たぶん〕
入荷は確か明日になるはずです
A fresh supply is due tomorrow, I believe.
確か５月末のことだった
It was at the end of May, if I remember correctly [rightly].